The iBookstore feed is a relative latecomer, arriving well after other Apple streams for the App Store and the rest of iTunes. The company has typically devoted less effort to marketing the iBookstore though, only mentioning it briefly in recent keynotes and TV ads. Despite being an official app, iBooks is also just an optional download for iOS devices. Its status may be linked to sales, since iBookstore revenues are still believed to be well below those for Amazon's Kindle e-books.